The Meteorological Office is blocking public scrutiny of the central role played by its top climate scientist in a highly controversial report by the beleaguered United Nations Intergovernmental Panel on Climate Change.

Professor John Mitchell, the Met Office’s Director of Climate Science, shared responsibility for the most worrying headline in the 2007 Nobel Prize-winning IPCC report – that the Earth is now hotter than at any time in the past 1,300 years.

And he approved the inclusion in the report of the famous ‘hockey stick’ graph, showing centuries of level or declining temperatures until a steep 20th Century rise.

By the time the 2007 report was being written, the graph had been heavily criticised by climate sceptics who had shown it minimised the ‘medieval warm period’ around 1000AD, when the Vikings established farming settlements in Greenland.

In fact, according to some scientists, the planet was then as warm, or even warmer, than it is today.